Optimizing MySQL Configuration

Optimizing MySQL Configuration
Peter Zaitsev,CEO
Technical Webinars Series
March 2012

Agenda
• MySQL Configuration Tuning Basics
• Tools to Configure MySQL
• Looking at Most Important Options
www.percona.com

Things to know about MySQL
configuration
• Default configuration is poor
– MySQL does not scale it with server size
• Understand what you're changing
– Google Copy/Paste without thinking can be bad
• Avoid Obsessive Tuning Disorder
– Setting 10 settings will give 95% of possible
performance in 95% cases
• Beware of “Sample Configs” In MySQL
distributions
– They are pretty outdated
– 2GB of memory is “huge” these days ?
www.percona.com

Most Options do not Scale
• Going to Server with 8x memory you can't just
multiply all configuration variables 8x
•16GB of memory to 128GB of memory
– sort_buffer_size 4MB to 32MB is bad idea.
www.percona.com

Know Scope and Unit
• sort_buffer_size=16G
– Wrong! sort_buffer_size is set per connection
• table_cache_size=64M
– Wrong! table_cache_size is set in elements
not memory size.
www.percona.com

Set Variables Locally
• Many Variables are SESSION
– Can be set for current session only
• Set variable value for session doing complex
queries instead of setting it globally:
mysql> set session sort_buffer_size=16*1024*1024;
Query OK, 0 rows affected (0.00 sec)
www.percona.com

Avoid Basic Mistakes
• Setting variables in wrong config file
– /etc/mysql/my.cnf instead of /etc/my.cnf
• These depend on Linux Distro, Beware
• Duplicating Options
– Last option will override previously set
• Not knowing Synonyms
– table_cache is same as table_open_cache
• Using wrong section for options
– Server reads [mysqld], client [mysql]
www.percona.com

Config Management Practices
• Keep Config Files in Sync on different servers
– Out of Sync config files is frequent cause of
mistakes and confusion
• Keep Record of Changes
– Config files under version control is great
– At least keep your changes documented
www.percona.com

Do not let MySQL Swap
• Allocating too much memory and having MySQL
swapping is a lot worse than not using all memory
• Monitor swapping (si/so from vmstat closely)
• Start with safe buffer values and increase them
gradually if a lot of memory stays free
pz@ubuntu:~$ vmstat 5
procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu---r
b swpd free buff cache si so bi bo in cs us sy id wa
1 0 0 2725708 253216 513572 0 0 1 1 20 22 0 0 100 0
0 0 0 2725700 253216 513596 0 0 0 0 72 73 0 0 100 0
0 0 0 2725700 253216 513596 0 0 0 3 70 74 0 0 99 1
0 0 0 2725700 253216 513596 0 0 0 0 70 74 0 0 100 0
0 0 0 2725700 253216 513596 0 0 0 0 70 74 0 0 100 0
0 0 0 2725700 253216 513596 0 0 0 0 70 72 0 0 100 0
www.percona.com

Agenda
• MySQL Configuration Tuning Basics
• Tools to Configure MySQL
• Looking at Most Important Options
www.percona.com

Automated Configuration Tuning
• Configuration Tuning Tools
–Tools which claim to create best configuration by
looking at status variables
• Advisory Tools
– Tools which check your config file for typical
mistakes and omissions
• Basic configuration creation tools
– Do not claim to do magic but can get your
started with better configuration than default
www.percona.com

mysqtuner
-------- General Statistics --------------------------------------------------
[--] Skipped version check for MySQLTuner script
[OK] Currently running supported MySQL version 5.1.57-rel12.8-log
[OK] Operating on 64-bit architecture
-------- Storage Engine Statistics -------------------------------------------
[--] Status: +Archive -BDB -Federated +InnoDB -ISAM -NDBCluster
[--] Data in MyISAM tables: 73G (Tables: 1282)
[--] Data in InnoDB tables: 1G (Tables: 338)
[--] Data in MEMORY tables: 0B (Tables: 2)
[!!] Total fragmented tables: 110
-------- Security Recommendations -------------------------------------------
[!!] User '@' has no password set.
www.percona.com

Mysqltuner (2)
-------- Performance Metrics -------------------------------------------------
• [--] Up for: 157d 10h 0m 23s (533M q [39.219 qps], 8M conn, TX: 1202B, RX:
146B)
• [--] Reads / Writes: 97% / 3%
• [--] Total buffers: 4.3G global + 2.7M per thread (200 max threads)
• [OK] Maximum possible memory usage: 4.8G (40% of installed RAM)
• [!!] Slow queries: 7% (41M/533M)
• [OK] Highest usage of available connections: 54% (109/200)
• [OK] Key buffer size / total MyISAM indexes: 4.0G/1.3G
• [OK] Key buffer hit rate: 100.0% (45B cached / 6M reads)
• [!!] Query cache is disabled
• [OK] Sorts requiring temporary tables: 0% (44K temp sorts / 60M sorts)
• [!!] Joins performed without indexes: 255685
• [!!] Temporary tables created on disk: 41% (25M on disk / 61M total)
• [OK] Thread cache hit rate: 91% (791K created / 8M connections)
• [!!] Table cache hit rate: 2% (1K open / 59K opened)
• [OK] Open file limit used: 32% (2K/8K)
• [OK] Table locks acquired immediately: 99% (436M immediate / 436M locks)
• [!!] InnoDB data size / buffer pool: 1.1G/256.0M
•
www.percona.com

mysqltuner(3)
-------- Recommendations -----------------------------------------------------
• General recommendations:
• Run OPTIMIZE TABLE to defragment tables for better performance
• Adjust your join queries to always utilize indexes
• When making adjustments, make tmp_table_size/max_heap_table_size equal
• Reduce your SELECT DISTINCT queries without LIMIT clauses
• Increase table_cache gradually to avoid file descriptor limits
• Variables to adjust:
• query_cache_size (>= 8M)
• join_buffer_size (> 128.0K, or always use indexes with joins)
• tmp_table_size (> 16M)
• max_heap_table_size (> 16M)
• table_cache (> 4096)
• innodb_buffer_pool_size (>= 1G)
www.percona.com

pt-variable-advisor
• # WARN innodb_flush_log_at_trx_commit-1: InnoDB is not configured in strictly ACID mode.
•
• # NOTE innodb_max_dirty_pages_pct: The innodb_max_dirty_pages_pct is lower than the default.
•
• # NOTE log_warnings-2: Log_warnings must be set greater than 1 to log unusual events such as
aborted connections.
•
• # NOTE max_connect_errors: max_connect_errors should probably be set as large as your
platform allows.
•
• # WARN old_passwords: Old-style passwords are insecure.
•
• # WARN slave_net_timeout: This variable is set too high.
•
• # NOTE innodb_data_file_path: Auto-extending InnoDB files can consume a lot of disk space that is
very difficult to reclaim later.
•
• # WARN myisam_recover_options: myisam_recover_options should be set to some value such as
BACKUP,FORCE to ensure that table corruption is noticed.
•
• # WARN sync_binlog: Binary logging is enabled, but sync_binlog isn't configured so that every
transaction is flushed to the binary log for durability.
www.percona.com

tools.percona.com
www.percona.com

Tools.percona.com
www.percona.com

Tools.percona.com
www.percona.com

Agenda
• MySQL Configuration Tuning Basics
• Tools to Configure MySQL
• Looking at Most Important Options
www.percona.com

Lets look at the options now
• Different classes of options:
– General Options
– MyISAM
– Innodb
– Visibility and Logging
www.percona.com

Getting Status Variables
• We refer to SHOW GLOBAL STATUS output in
many descriptions
• Percona Toolkit too pt-mext is helpful
• pt-mext -r -- mysqladmin ext -i100 -c4
• Aborted_clients 128 0 0
Aborted_connects 909 0 0
Binlog_cache_disk_use 3 0 0
Binlog_cache_use 262857 0 0
Bytes_received 146518902681 580976 459113
Bytes_sent 1202983049426 1417886 1018617
www.percona.com

General Options
• max_connections
– How many connections to allow ? Watch
max_used_connections status value
• thread_cache
– Cache to prevent excessive thread creation
– 50-100 is good value. Watch threads_created
• table_cache/table_open_cache
– Cache of opened table instances
– Single table may have multiple entries
– Watch opened_tables status value
– Start with 4096
• MySQL will only use as needed anyway.
www.percona.com

General Options
• open_files_limit
– MyISAM tables require up to 2 file handlers
– Each connection is file handler too
– Safe to set to 65535 in most systems
• table_definition_cache
– Cache table definitions (CREATE TABLE)
– Only one entry per table
– Watch Opened_table_definitions
– Set to number of tables + 10% unless 50K+
tables
www.percona.com

General Options
• back_log
– Need adjustment if many connections/sec
– 2048 is reasonable value
• max_allowed_packet
– Limits maximum size of query
– Limits internal string variable size
– 16MB is a good value
• max_connect_errors
– Prevent password brute force attack
– Can cause “Host Blocked” error messages
– Value around 1000000 is good
www.percona.com

General Options
• skip_name_resolve
– Avoid DNS lookup on connection. Faster and
Safer
– Do not use host names in GRANTs
• old_passwords
– Should NOT be enabled. Will cause insecure
password hash to be used.
www.percona.com

General Options
• log_bin
– Enable for replication and point in time recovery
– Set to “mysql-bin” to avoid default naming
• sync_binlog
– Make Binlog durable. Set to 1 if have RAID
with BBU or Flash
•Can be really performance killer with slow
drives.
• expire_log_days
– Purge old binary logs after this number of days
– 14 (2 weeks) is a good value with weekly
backups.
www.percona.com

General Options
• tmp_table_size
• max_heap_table_size
– Typically set to same value (workload based)
– Created_tmp_disk_tables status variable
• Beware BLOB/TEXT fields cause on disk
table with any size.
• query_cache_size
– Enable query cache only if it is tested to provide
significant gains
– Often causes stalls and contention
– Do not set over 512MB
www.percona.com

General Options
• sort_buffer_size
– In memory buffer used for sorting
– Watch sort_merge_passes
– Consider setting for session for large queries
– Values up to 1MB are good default
– Large values hurt performance of small queries
• join_buffer_size
– Helps performance of Joins with no indexes
– Better get rid of such Joins !
– 8MB can be reasonable value
• default_storage_engine
– Use this engine for tables if not specified
www.percona.com

General Options
• read_rnd_buffer_size
– Buffer for reading rows in sorted offer
– Specifies Maximum Value
– Values around 16MB often make sense
– Do not mix with read_buffer_size
• Tmpdir
– Specify location of temporary directory
– Tmpfs often good choice unless very large
temporary space is needed.
•tmpdir=/dev/shm
www.percona.com

MyISAM options
• key_buffer_size
– Cache MyISAM Indexes.
– Does Not cache data.
– Up to 30% of memory if using MyISAM only
• myisam_recover
– Automatically repair corrupted MyISAM tables
after crash. BACKUP,FORCE is a good value.
• myisam_sort_buffer_size
– Buffer used for building MyISAM indexes by
Sort. 8MB-256MB are good values.
www.percona.com

MyISAM Options
• low_priority_updates
– Allow higher concurrency for SELECTs
– May starve update queries
• bulk_insert_buffer_size
– Buffer to optimize Bulk Inserts
– Values of ¼ of key_buffer_size make sense
– Note it is per connection value
www.percona.com

Innodb – Memory Settings
• innodb_buffer_pool_size
–The most important setting. Often 80%+ of
memory is allocated here.
• innodb_buffer_pool_instances
– Reduce contention. Set to 4+ in MySQL 5.5+
• innodb_log_buffer_size
– Buffer for log files. Good Values 4MB-128MB
– Not only reduce writes but help contention
• innodb_ibuf_max_size
– Control size of Insert buffer. Default is ½ of
Buffer pool. Smaller values are good for SSD
www.percona.com

Innodb IO Options
• innodb_flush_log_at_trx_commit
– Control Durability
– 1=flush and sync; 2=flush; 0=neither
• Innodb_flush_method
– Controls how Innodb Performs IO
– O_DIRECT good value for most servers
• innodb_auto_lru_dump
– Percona Server Feature to warmup quickly
– 300 (seconds) is a good value
• innodb_io_capacity
– Controls Innodb Assumption about Disk
Performance. Increase for faster drives.
www.percona.com

Innodb IO Options
• innodb_read_io_threads
• innodb_write_io_threads
–Control number of threads doing reads and
writes
– MySQL 5.5 has async IO so very high values
might not be needed
– 4 is good default. Higher for large IO systems.
• innodb_flush_neighbor_pages
– Percona Server feature to control how flushing
works
– Disable (set to 0) for SSD
www.percona.com

Other Innodb Options
• innodb_log_file_size
– Size of redo log file. Larger logs better
performance but longer recovery.
• innodb_log_files_in_group
– Leave at 2 which is default.
• innodb_file_per_table
– Store each Innodb table in separate file. Usually
Good choice
• innodb=force
– Enable so MySQL does not start if Innodb could
not initialize. Otherwise it might start but error on
access to all Innodb tables.
www.percona.com

Other Innodb Options
• innodb_data_file_path
– Settings for Innodb System Tablespace
– Use one file. Limit growth as you can't shrink it
– ibdata1:10M:autoextend:max:10G
• innodb_lock_wait_timeout
– How long to wait for row level locks before
bailing out ?
• innodb_old_blocks_time
– Helps to make buffer pool scan resistant
– Values around 1000 make sense
www.percona.com

Other Innodb Options
• innodb_file_format
– Which file format Innodb will use
– “Antelope” is default legacy format
–“Barracuda” allows to use new features like
compression
• innodb_stats_on_metadata
– Update statistics on meta data access
– Such as Information_schema queries
– Typically best disabled for more workloads
•Set to 0
– Innodb will still refresh stats when table
changes significantly
www.percona.com

Visibility Options
• performance_schema
– Enable Performance Schema in MySQL 5.5+
– Watch potential overhead.
• log_slow_queries
– Enable Slow Query Log. Old but very helpful.
• long_query_time
– Especially with long_query_time set to 0
periodically to get sample of the load
• log_slow_verbosity=full
– Get a lot more data about queries in Percona
Server
www.percona.com

Visibility Options
• low_warnings=2
– Get warnings about disconnects and other
minor issues in error log.
– More information but it can get spammy
• userstat_running=1
– Get advanced Table and Index usage statistics
in Percona Server and MariaDB
www.percona.com

Summary
• Many Options to chose from !
• Close to 400 variables available In latest versions
• Remember in most cases you do not need to tune
more than a few
• Consider starting with config file generated by
http://tools.percona.com
– At least it will show you which options to pay
attention to first.
www.percona.com

Resources
● High Performance MySQL
● Third edition in a matter of days!
● http://www.highperfmysql.com/
● Percona Training
● http://www.percona.com/training/
● Dallas,TX May14-17
● Percona Webinars
● http://www.percona.com/webinars/
● Mar 28: Monitoring MySQL with Percona Monitoring Plugins
● Apr 4: Percona XtraDB Cluster
www.percona.com

● Percona Toolkit
Resources
● pt-visual-explain tool makes EXPLAIN readable
● http://www.percona.com/software/
● Percona Online Tools
● http://tools.percona.com/
● Generate my.cnf files easily
● Get advice on SQL
● Percona Career Center (Yes, We're Hiring!)
● www.percona.com/about-us/careers/
www.percona.com

MySQL Conference & Expo
April 10-12, Santa Clara
www.percona.com/live
Use “Webinar-PL” code for 10% off
Peter Zaitsev
pz@percona.com